Gzip Compression Checker

We fetch your page advertising support for gzip, deflate, and Brotli — measure how many bytes arrive on the wire, decompress them, and compare with the uncompressed size to show your real transfer savings. We also do an identity-encoding probe to catch misconfigured servers.

HTTP Content Compression: Brotli (br) vs. Gzip (gzip) Standards

HTTP compression reduces the raw byte payload transferred over the network between web servers and client browsers. Enabling modern compression algorithms on text-based assets (HTML, CSS, JavaScript, JSON, SVG) routinely reduces bandwidth consumption by 65% to 85%, accelerating Time-To-First-Byte (TTFB) and improving Core Web Vitals.

Compression Algorithm Specifications

1. Brotli Compression (Content-Encoding: br)

Standardized under IETF RFC 7932, Brotli uses a combination of the LZ77 algorithm, Huffman coding, and 2nd-order context modeling with a built-in 120 KB static dictionary. Brotli produces payloads roughly 15% to 25% smaller than Gzip at equivalent CPU compression levels.

2. Gzip Compression (Content-Encoding: gzip)

Standardized under IETF RFC 1952, Gzip utilizes the DEFLATE algorithm. Gzip is universally supported across every browser and legacy HTTP client.

Server Configuration Examples

Nginx (Brotli + Gzip Fallback)

# Enable Gzip
gzip on;
gzip_comp_level 6;
gzip_min_length 256;
gzip_types text/plain text/css application/json application/javascript application/xml image/svg+xml;

# Enable Brotli (ngx_brotli module)
brotli on;
brotli_comp_level 6;
brotli_types text/plain text/css application/json application/javascript application/xml image/svg+xml;

The Importance of the Vary: Accept-Encoding Header

When dynamic compression is enabled, servers must send the Vary: Accept-Encoding header. This instructs intermediate caching proxies and CDNs to store separate cached copies of the resource for clients supporting Brotli (br), Gzip (gzip), or uncompressed (identity), preventing corrupted responses from being delivered to legacy clients.

Frequently Asked Questions

Should media assets (JPEG, WebP, MP4) be compressed with Gzip?

No. Image, video, and audio formats are already compressed with domain-specific binary codecs. Attempting to Gzip or Brotli compress JPEGs or WebP images wastes CPU cycles and can occasionally increase file size.

What is the Identity-Encoding probe?

An Accept-Encoding: identity probe tests whether a server correctly respects client requests for raw uncompressed bytes. Servers that return compressed data despite an explicit identity header violate RFC 9110 specifications.

How does compression affect page load performance?

Smaller transfer sizes reduce network round trips and packet latency. Measure your total transfer weight with our Page Size Checker and audit end-to-end rendering speed with our Page Speed Checker.